In-face InN films were grown heteroepitaxially on (0001) GaN/Al2O3 templates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). Films’ properties were investigated by high resolution x-ray diffraction, photoluminescence, atomic force microscopy, transmission electron microscopy, scanning electron microscopy and Hall effect measurements.
A physical model of InN growth by RF-MBE is presented and the optimization of InN growth conditions is discussed in the model’s context. High quality InN films were grown under optimized conditions. They exhibit a step-flow morphology with surface rms roughness as low as 0.20 nm, x-ray diffraction rocking curve linewidths of approximately 350 and 300 arcsec for the symmetric (0004) and the asymmetric (10-15) reflections, respectively, and electron mobilities in the range of 1500 cm2/V∙sec for carriers concentration in the low 1018 cm-3.
The c and α lattice parameters were dependent on the growth conditions. The c versus a relation exhibited a linear behavior indicative of the presence of biaxial strain. From the data a Poisson ration equal to 0.42+-0.05 was determined for the case of InN.
All samples exhibited intense photoluminescence with clear evidence of the Burstein-Moss effect. Transitions to acceptor states were identified in several samples. The intensity of luminescence depended on the growth conditions and it was enhanced of the case of films grown with a two-step process and with near stoichiometric III/V flux ratio.
Electron microscopy observations revealed the abruptness of the InN/GaN interface and the relaxation of most of the misfit stress by a network of misfit dislocations at the InN/GaN interface. Determination of lattice constants and misfit dislocation periodicity were in agreement with the X-ray measurements.